A large number of 3D fabric forming processes have been developed in the past 50 years, especially for producing textile reinforcements for manufacturing composite materials. A 3D fabric is defined as a single-fabric system (i.e. not stitched sheets/layers of fabrics), the constituent yarns/tows of which are supposed to be disposed in a three mutually perpendicular planes relationship. Accordingly, a 3D fabric can be produced using one or more sets of yarns.
Most methods aim to essentially arrange and integrate three sets of yarns/tows orthogonally, i.e. in XYZ (i.e. length, width and thickness) directions. Some methods additionally incorporate additional yarns in bias directions relative to fabric-length direction (whereby such 3D fabrics comprise five sets of yarns). Technically all such methods can be classified as 3D-weaving (U.S. Pat. Nos. 6,186,185 and 6,338,367) and non-woven “noobing” (EP 0236500, U.S. Pat. No. 5,465,760, WO 9803712, U.S. Pat. Nos. 6,315,007, 5,353,844, FR 2227748, U.S. Pat. Nos. 5,343,897, 5,449,025, 5,435,352, 5,327,621, 5,270,094, 4,336,296, 3,834,424, 5,137,058, SE 9500309, U.S. Pat. Nos. 5,242,768, 3,818,951, 5,085,252, 3,955,602, 4,518,640, 5,465,760, 5,270,094, 4,872,323etc.) types, as established by Khokar [1-3].
The main technical difference between the 3D-weaving and non-woven “noobing” processes resides in the fundamental technical fact that the shedding operation is foremost and indispensable for technical realization of the weaving process and woven (interlaced) material. Accordingly, the 3D-weaving process is technically realizable by employing only the dual-directional shedding operation (U.S. Pat. Nos. 6,186,185 and 6,338,367) to create sheds in fabric's thickness and width directions (compared with the conventional 2D-weaving process wherein the mono-directional shedding operation is employed to realize the process by creating a shed in only the fabric's width direction). It may be noted that exploitation of conventional 2D-weaving process for producing a 3D fabric does not make it the 3D-weaving process. This is because the 2D-weaving process remains identical whether producing 2D fabric or 3D fabric and both these types are composed of a set of warps interlacing with a set of wefts. In comparison, the 3D fabric produced by the 3D-weaving process is composed of a set of warps interlacing with two sets of mutually perpendicular wefts—one interlacing in fabric's thickness direction and the other in fabric's width direction. The non-woven noobing process, on the other hand, is realized without involving any shedding operation. As a consequence, the 3D fabrics producible by the 3D-weaving and the non-woven noobing processes respectively have the characteristic interlaced (woven) and non-interlaced (noobed) structures. However, this fundamental difference has been overlooked in the past and without any technical basis the noobing process was assumed and misrepresented as 3D-weaving until they were technically described, clarified and characterized by Khokar [1-3].
It is relevant here to give details in brief of the noobing process which is unique in that it produces only 3D fabrics. Unlike other fabric-forming processes the noobing process can neither produce 2D fabrics (such as woven, braided and knitted sheet fabrics) nor 2.5D fabrics (such as pile, plush and terry fabrics). The noobing process essentially involves binding a set of stacked unidirectional yarns (X), the orientation of which is usually in fabric's length direction, using two other sets of binding yarns (Y) and (Z). Each of these sets of binding yarns is oriented in the stacked unidirectional yarns' width direction (Y) and thickness direction (Z). The structural integrity of the 3D fabric is realized by cyclically binding the set of unidirectional yarns (X) with binding yarns (Y) and (Z). The binding yarns of the sets (Y) and (Z) connect with their respective directions' opposite exterior yarns of the stacked unidirectional yarns (X). The created bindings therefore occur at the surfaces/exteriors of the produced 3D fabric. The yarns of the sets (X), (Y) and (Z) occur linearly, or straight, between their respective directions' opposite surfaces of the produced 3D fabric. In another variant of noobing process, sets of yarns oriented in fabric's length (X), width (Y) and two bias (+/−β) directions are stacked and then bound by using another set of yarns (Z) which are oriented in the stacked yarns' thickness direction. Inclusion of the two sets of bias yarns (+/−β), which lie between the two longitudinal edges of the 3D fabric at an angle other than 90° with respect to the longitudinal edges, is done to improve the mechanical performance of the 3D fabric to meet application demands. As can be noted now, binding of one (uniaxial) or more (multiaxial) directionally oriented sets of stacked yarns is indispensable to the noobing process whereby the noobing process stands technically differentiated from the weaving, knitting, braiding and all known non-woven processes.
Accordingly, the former process type is referred to as the uniaxial noobing process and the latter is called the multiaxial noobing process (which is commercially employed to produce the so-called multiaxial non-crimp fabrics). The 3D fabrics produced by both these process types are henceforth respectively called uniaxial noobed fabric and multiaxial noobed fabric. Both these types of noobed fabrics are fundamentally a 3D fabric because they invariably comprise three and five sets of yarns (X, Y, Z in former and X, Y, Z and +/−β in latter) respectively, which are disposed in a three mutually perpendicular planes relationship. In either case, the longitudinal direction yarns (X) are supplied individually and bound into the 3D fabric directly. As all the constituent yarns of both the noobed fabric types occur linearly, i.e. without interlacing, intertwining and, interlooping, the structural integrity of the noobed fabrics comes from the bindings at its surfaces. Clearly, because noobed fabrics are technically different from woven, braided and knitted fabrics, the noobing process is also therefore technically unlike weaving, knitting, braiding and all known non-woven processes.